Genetic and environmental influences on reading and listening comprehension

Abstract

We report preliminary behaviour genetic analyses of reading and listening comprehension from The Colorado Learning Disabilities Research Center. Although the twin sample with these new measures is still of limited size, we find substantial, and significant, genetic influences on individual differences in both reading and listening comprehension. In addition, word recognition and listening comprehension each accounted for significant independent genetic influences on reading comprehension. Together, they accounted for all the genetic influence on reading comprehension, indicating a largely genetic basis for the 'simple model' of individual differences in reading comprehension proposed by Hoover and Gough (1990).When we began our behaviour genetic studies of 'dyslexia', or reading disability, with identical and fraternal twins in 1982, it was commonly assumed that the difficulties in reading comprehension that children with dyslexia have are largely, if not completely, because of their deficits in phonological skills and word decoding (Liberman, Shankweiler, Fisher & Carter, 1974;Perfetti, 1985;Shankweiler, 1989). For example, in Perfetti's 'verbal efficiency theory', the higher processing demands in word decoding in poor readers were thought to result in fewer resources for processing the meaning of text, resulting in deficits in their reading comprehension. However, in recent years, evidence has been accumulating to support some dissociation between decoding and comprehension problems. This raises the question of the extent to which deficits in decoding and comprehension share a common aetiology. The purpose of this report is to provide preliminary findings in our attempt to address this question by examining the genetic and environmental aetiologies of individual differences in comprehension. Relation between word decoding and comprehension problemsEarly research by Curtis (1980) found that while word decoding and reading comprehension are very highly correlated in beginning readers, this correlation declines

Word reading and reading comprehension: stability, overlap and independence

“…However, our results are consistent with those of Keenan, Betjemann, Wadsworth et al (2006) and Wadsworth et al (2001Wadsworth et al ( , 2006, who found negligible shared environmental influences in older children. Moreover, even in much younger children, Byrne and colleagues also report that shared environmental effects found in kindergarten were no longer significant by the end of first grade (Byrne et al, 2007).…”

“…Between measures, a high proportion of the covariance of reading comprehension and word reading was due to shared genetic factors, but we also noted a significant genetic factor unique to reading comprehension at both time points, independent of word reading. This supports the recent findings of Keenan and colleagues (Keenan, Betjemann, Wadsworth et al, 2006), who also observed a unique genetic factor for reading and listening comprehension. It suggests that while many of the genetic influences on reading comprehension and word reading are overlapping, there are unique genetic influences on comprehension processes, supporting the argument that reading comprehension skills may be unique and separable from word reading skills (e.g., Cain et al, 2000;Catts et al, 2003;Gough et al, 1996;Gough & Tunmer, 1986;Hoover & Gough, 1990;Leach et al, 2003;Nation, 2005;Oakhill et al, 2003).…”

“…For example, some studies have found children who have comprehension deficits with normal word reading skills (Cain, Oakhill, & Bryant, 2000;Catts, Hogan, & Fey, 2003;Nation, 2005;Oakhill, Cain, & Bryant, 2003); others have found children with normal reading comprehension but selective word reading deficits (Leach et al, 2003). The results of a behavioral genetic study by Keenan, Betjemann, Wadsworth et al (2006) also support the partial independence of word reading and comprehension skills. Keenan and colleagues found a genetic factor common to comprehension and word reading, but also found a second significant genetic factor for comprehension, independent from word reading.…”

“…Univariate heritability estimates for word reading skill and related reading components range from .30 to .85 (e.g., Byrne et al, 2005a;DeFries et al, 1997;Gayán & Olson, 2003;Harlaar, Spinath, Dale, & Plomin, 2005;Petrill, Deater-Deckard, Thompson, DeThorne, & Schatschneider, 2006a;Stevenson, Graham, Fredman, & McLoughlin, 1987;Tiu, Wadsworth, Olson, & DeFries, 2004;Wadsworth, Corley, Hewitt, & DeFries, 2001;Wadsworth, Corley, Plomin, Hewitt, & DeFries, 2006). While word reading and its related components are most often studied, some researchers have also assessed genetic influences on reading comprehension and have noted similar heritability estimates, in the range of .41 to .76 (e.g., Byrne et al, 2005b;Harlaar, Dale, & Plomin, 2007;Keenan, Betjemann, Wadsworth, DeFries, & Olson, 2006;Petrill, Deater-Deckard, Thompson, Schatschneider, DeThorne, & Vandenbergh, 2007). Given that word reading and comprehension skills are both stable and heritable, we hypothesize that this stability may be due to genetic influences.…”

Individual differences, rereading, and self-explanation: Concurrent processing and cue validity as constraints on metacomprehension accuracy

“…Reading ability will impact the difficulty of the primary object-level task of text processing. Some readers struggle with one or more of the subprocesses involved in comprehension (e.g., Keenan, Betjemann, Wadsworth, DeFries, & Olson, 2006;Perfetti, 1985;Yuill & Oakhill, 1991). Thus, they should be limited in their ability to concurrently carry out the task of monitoring.…”